Known friction clutches provide a releasable torsional connection between a motor vehicle engine flywheel and an associated transmission. Repeated clutch disengagement and engagement cycles wear the friction material of the clutch driven disc. The wear results in a change in the axial location of the pressure plate in the engaged position. The shift in axial location results in a progressive decrease in the clutch engagement force or clamping load. Clutches are commonly provided with adjustment mechanisms to compensate for such wear.
The clutch clamping load is generated by a spring acting directly or indirectly against the pressure plate and reacting directly or indirectly against the clutch cover.
One type of spring configuration employs a diaphragm spring having an annular portion with radially inwardly directed fingers extending from the annular portion. The radially innermost tips of the fingers engage a release bearing and bow to deflect the annular portion, and thereby release the clutch, when the release bearing is axially displaced.
Another type of clutch spring configuration applies a spring load to a plurality of radially oriented levers which in turn engage the pressure plate. If compressive coil or angle springs are employed, the spring load is commonly applied to a radially inner end of the levers. The levers are pivotally supported at the radially outer ends. Clutches may employ diaphragm springs in place of coil springs to bias the levers.
As the friction material wears, the engaged position of the radially inner finger or lever tips moves closer to the flywheel. Adjustment mechanisms disposed between the cover and the levers or between the pressure plate and the diaphragm spring compensate for this change.
One type of known adjustment mechanism relies on the relative rotation of two annular cams, each having inclined cam surfaces in engagement with each other. The relative rotation of the cams compensate for wear of the friction material. The cams are biased to rotate in a direction that increases a combined height or thickness of the cam portions. The rotative biasing force is induced by a torsional biasing spring functionally disposed between the two cams. A number of different spring configurations have been employed in this capacity, including coil tension springs, torsional round wire springs, and torsional flat wire springs.
The torsional wire spring, in both round and flat cross section varieties, is particularly advantageous for use as a cam biasing spring, in that it takes up very little space. The flat wire spring is, in one embodiment, radially disposed between an axially extending wall of the pressure plate and a rotatable cam member. A first end of the flat wire spring is fixed to the pressure plate, and a second end of the flat wire spring is fixed to the rotating cam. The spring is hand coiled into the clutch. However, hand coiling the springs is difficult and time-consuming. Additionally, it has been demonstrated that flat wire springs may overlap their coils during operation, reducing the torsional load applied by the spring to the rotatable cam member, and potentially rendering the adjustment mechanism ineffective.
It is desired to provide a mechanism facilitating easier installation of torsional wire springs in a clutch.
It is desired to provide a mechanism which prevents axial overlap of the flat wire spring coils.
It is desired to provide a mechanism which keeps the coils of a torsional wire spring substantially centered with respect to the axis of rotation of the clutch and prevents the interference of the spring coils with adjacent features and/or mechanisms of the clutch.